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SUMMARY:Boltzmann in materials - tales of heat and electricity\, the death
  of phonons\, and the birth of relaxons
DTSTART:20160530T103000
DTSTAMP:20260916T220422Z
UID:1f56f973cc388684fbbf822cc75e3d4e3e50c6b45152b05c87eebb52
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. N. Marzari & A. Cepellotti\, National Centre for Compete
 nce in Research NCCR MARVEL\, EPFL\nQuantum-mechanical simulations are dri
 ving a revolution in our capabilities to understand\, predict\, and design
  the properties and performance of novel materials and devices\, and I'll 
 try and illustrate this paradigm\, both with an introduction to the field\
 , and then focusing on electrical and thermal transport\, showing how dens
 ity-functional theory and density-functional perturbation theory can provi
 de us with accurate thermomechanical properties\, many-body perturbation t
 heory with electronic spectra\, and how phonon lifetimes and electron scat
 tering rates can endow with predictive accuracy the Boltzmann transport eq
 uation for electrons and phonons in crystalline materials.\nIn the process
 \, I will highlight how in two-dimensional materials normal heat-flux cons
 erving processes dominate over Umklapp scattering. As a result\, the phono
 n gas behaves as an ideal fluid and novel regimes emerge\, with collective
  excitations carrying heat over macroscopic system sizes and Poiseuille an
 d Ziman hydrodynamics\, hitherto confined to cryogenic temperatures\, char
 acterizing transport at ordinary conditions. In several cases wave-like he
 at transfer appears in addition to ballistic or diffusive propagation\, wh
 ere second sound may be present at room temperature. Most importantly\, th
 is analysis will underline why we cannot consider phonons as the heat carr
 iers in crystals\, and how we can construct a kinetic theory of heat trans
 port through novel excitations - termed here relaxons.
LOCATION:PPB 019
STATUS:CONFIRMED
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